Our invention relates generally to electric coil devices having a coil or coils wound around a core, and particularly to those suitable for use as transformers of switching regulators. However, we do not wish out invention to be limited to this particular application as the coil devices constructed according to our invention lend themselves to use as chokes and to additional applications.
Conventionally, in a typical small size transformer, the primary and the secondary windings have been arranged concentrically around a flanged bobbin sleeved upon a core. The primary and the secondary windings have been insulated from each other with three or more sheets or layers of special paper. Insulating spacers, known as barriers, have been placed next to the bobbin flanges. Insulating tubes have also been sleeved upon the leads of the primary winding.
We object to the use of the insulating paper, barriers and tubes as they make difficult and troublesome the assemblage of the transformer. Moreover, the insulating paper and barriers add considerably to the size of the transformer. It is also a disadvantage that the three or more sheets or layers of insulating paper increases the distance between the primary and the secondary windings, with a consequent decrease in electromagnetic coupling therebetween.
Japanese Unexamined Patent Publication No. 62-293705 represents a solution to this problem. It teaches to dispense with the insulating paper, barriers and tubes by use of insulated conductors for the primary and the secondary windings.
We object to this known solution, too. It has been very difficult to enclose conductor wires in coverings that are sufficiently thin but can well perform the functions for which they are intended. Consequently, the transformers made with such insulated conductors have not been reduced so much in size, or have not been so favorable in performance characteristics, as could be desired. The insulated conductors have also offered the disadvantage that parts of the insulating coverings have had to be removed to expose the corresponding parts of the conductors for connection to terminals. Such removal of the insulating coverings has represented a substantial impediment to the ease of manufacture of the transformers.